1. Field of the Invention
The present invention relates to a method of and apparatus for scanning tape with a scanning head, and more particularly to such a method and apparatus for use in recording and/or playing back video signals on an elongated recording medium, such as magnetic tape.
2. Description of the Prior Art
Conventional video signal record and/or playback systems for recording and/or playing back video signals under raster scanning system, such as television signals, include the vertical track scanning system, such as the four-head video recording system provided by Ampex Corporation, the helical scanning system, and the arc track scanning system, for example. Home video cassette recorders, typically employ the helical scanning. The helical scanning system is advantageous in that track patterns are formed in straight on a tape with a certain video track angle maintained with respect to the longitudinal direction of the tape, giving rise to higher recording density per unit length of tape, variable recording density dependent upon the video track angle, and a closer and more uniform contact of a video head with the tape.
In the helical scanning system, however, a recording tape runs in contact with a rotary drum of magnetic heads with a certain angle maintained between the longitudinal direction of the tape and the circumferencial direction of the head drum. In order to accomplish a stable running of the tape on the magnetic head, however, precise and accurate adjustment may be required in the head assembly and tape driving mechanism.
With a video cassette system using a video tape cassette, a stable driving of tape requires the tape to be oriented or directed essentially both at the exit from the tape supply reel and at the entrance to the tape winding reel of the cassette in such a manner that the tape runs at a constant height and in parallel with respect to a reference plane, which is parallel to a main surface of the tape cassette, with the sidewise direction of the tape perpendicular to the reference plane. For that purpose, the so-called VHS system, for example, employs the so-called M-type loading, in which the tape guiding system essentially includes a magnetic head rotary drum inclined with respect to a tape by a predetermined angle, a pair of tape guide posts provided in slant near the periphery of the rotary drum and far from the imaginary line connecting the exit and the entrance, and a pair of vertical posts for maintaining a part of the tape in contact therewith by a predetermined angle. This is complicated in structure. In addition, in order to make a close contact with a portion of tape on a part of the circumferential surface of the rotary drum by means of the pair of guide posts inclined with respect to the reference plane, and to maintain the height of the tape with respect to the reference plane constant with a tolerance of submicrometers, extensive accuracy is required in manufacturing and mechanically adjusting the elements involved in the tape running mechanism.
In order to increase recording capacity per video cassette, it is also required to design video tape which is very thin, for example, less than twenty micrometers thick. Such thin video tape is so insufficient in strength of the base material used as to fail to oppose the forces raised in the longitudinal direction of the pair of guide posts. Therefore, an edge of the tape may sometimes ride the flanges of the posts. In the case of a video cassette recorder using a thinner tape material, mechanical accuracy should be much more increased in the tape running mechanism.